Electrolytic marking medium



March 3, 1964 OPTICAL DENSITY G. MANDEL ETAL 3,123,542

ELECTROLYTIC MARKING MEDIUM Filed Oct. 13. 1960 CURVE 4 CURVE 2 8 3 CURVE l CURRENT INVENTORS GERALD MANUEL IRVING MNO LIEBLIQII- l BYE. A jl GZLDS EIN ATTORNEY United States Patent 3,123,542 ELEQTROLYTIC MARKING MEDlUl /i Gerald Mandel, New Rochelle, Irving Lieblich, Elmhurst, and Amnon Goldstein, New York, N.Y., assiguors to Hogan Faximile Corporation, New York, N.Y.

Filed Oct. 13, 1960, Ser. No. 62,423 15 Claims. (Cl. 2tl42) This invention relates to the art of electro-sensitive recording media and relates particularly to an improved recording medium employing a new marking compound. The invention is concerned especially with a novel electrolytic recording method which does not involve or depend upon lake-forming marking compounds and which does not involve or depend upon the format-ion of a color lake on the recording medium in order to obtain marking of the medium.

Heretofore, certain polyhydroxyphenolic compounds such as pyrocatechin (i.e., cateehol) have been discovered to be capable of serving as marking compounds in aqueous electrolytic recording papers such as disclosed in US. Patent No. 2,339,267 to J. V. L Hogan et al. and US. Patent No. 2,358,839 to E. R. Wagner. Such papers may be employed in electrical recording apparatus such as described in US. Patent No. 2,575,959 to I. V. L. Hogan. The method and principle of operation, by which all of the aforementioned polyhydroxyphenolic compounds and their derivatives serve to produce a mark on the recording medium, is described in these patents as involving the formation of a color lake on the medium which constitutes the mark. The aforesaid polyhydroxyphenolic compounds and derivatives are disclosed as being selected for their lake-forming characteristic.

Recording paper of the electrolytic type is generally marked by disposing the paper between a positive metal anode electrode and a negative cathode electrode. The paper is impregnated with an electrolytic solution containing as one ingredient a marking compound. Speak ing generally, when a voltage is applied between the elec: trodes and current flows through the paper, the marking compound is capable of reacting with ions supplied by the anode to form a colored mark on the surface of the paper wherever the anode contacts the paper adjacent to the cathode disposed on the other side of the paper.

In order to prove acceptable for various facsimile and related recording purposes, the recording paper must meet certain important requirements. The paper is preferably white initially and must have the ability to produce marks having a density which is a function, preferably linear, of the current passed through the paper. The color tone obtained should be able to vary uniformly in a range from white (i.e., for zero current flow) through grays (i.e., for currents of intermediate magnitudes) to black (i.e., for high or maximum current magnitude). Marks having a substantially purple, green or brown cast are generally not desirable. There also should be a minimum of bleeding or fringing of the mark so as to maintain sharp detail for the mark. The wet paper, while stored in a special container for extended periods of time prior to use, must remain stable (fresh) without chemical decomposition of its ingredients which would cause discoloration of the paper prior to use and would leave a discolored background after recording.

Moreover, it is very important to employ a recording paper capable of yielding a recorded copy which will re- 7 "ice chines involving exposure to ultra-violet light, such as an Ozalid machine.

Another very important consideration is the provision of a recording paper wherein the marking compound or other active ingredients in the paper will not diffuse or transfer, during or after recording, to adjacent sheets or surfaces of marked or unmarked paper nor to adjacent areas such as the walls of the recorder cabinet or of the room itself. Such transfer frequently results in an objectionable discoloration of the adjacent paper surfaces and walls.

In certain applications difficulty has been experienced in the past with the use of recording papers employing pyrocatechin (cateehol) as the marking compound. An especially troublesome problem in the use of cateehol recording papers is the tendency for the cateehol to diffuse or transfer to, and to discolor, adjacent sheets of paper and other surfaces adjacent to the recorder during and after recording. In order to obtain marks of full density when using the cateehol recording papers disclosed in the aforementioned patents, it has generally been found necessary to provide an electrical heater device adjacent to the paper after it passes from between the electrodes. The action of such a heater device increases still further the transfer characteristic of the cateehol.

While it is true that certain prior patents, such as US. Patent No. 2,339,267 supra, suggest that various chlorides and bromides may be used as the electrolyte in place of a nitrate, nevertheless subsequent experience through the years has revealed to the art that no chloride or bromide could be successfully employed as the electroiyte in these electrolyte recording media. The reason is that the recorded copy obtained from paper containing any chloride or bromide as the electrolyte, in combination with any specific marking compound hitherto em ployed, was invariably found to become streaked during and after recording. Consequently, to avoid streaking it has been the general practice to utilize a nitrate, such as potassium nitrate, as the electrolyte in recording papers. Recording papers containing the various nitrates as electrolytes are unfortunately light-sensitive in that they discolor after exposure to light, particularly ultra-violet rays, during and after recording, such as when the recorded copy is stored or run through an Ozalid duplicator machine or the like.

It is therefore an object of the invention to provide improved electro-responsive graphic recording media.

It is another object to provide electro-sensitive recording media containing as a marking compound a compound which heretofore has not been employed for this purpose.

It is another object to provide a new electrolytic recording method and media which does not depend upon lake-forming compounds nor the formation of color lake in order to mark the media.

It is another object to provide new electro-sensitive recording media wherein there is no external diffusion or transfer of the ingredients of the media during or after recording.

A further object is to provide a white electrolytic recording medium which does;not contain cateehol but rather contains a new substantially colorless marking compound which, both before and after recording, does not produce a discoloration in the background of the medium. 7

Another object is to provide an electrolytic recording media which contains a marking compound other than catechol and yet still provides a mark having a color tone which includes a range of gray colors up to and including dense .black rather than providing a mark which is more purple, red or brown than it is black.

It is a further object to provide electrolytic recording media which is chemically stable prior to use and which will remain stable to light both during and after recording and which will permit the recorded copy to be exposed repeatedly to ultra-violet light in a duplicating machine.

it is an especially important object to provide electrolytic recording media with a new marking compound which is capable of being used with any bromide or chloride as the electrolyte without the medium becoming unstable to light (including ultra-violet light) or streaking during or after recording as heretofore experienced.

Other objects and advantages of the invention will be apparent to those skilled in the art.

In a co-pending application Serial No. 4,629, filed January 26, 1960, by Gerald Mandel, and now U.S. Patent 3,024,173, one of the co-inventors herein, protocatechuic acid (hereinafter termed PCA) is disclosed as a marking compound and as accomplishing the foregoing objects.

In accordance with the present invention, we have discovered compounds which maybe substituted for the protocatechuic acid of the prior application in accomplish.- ing the foregoing objects. The new marking agents are polyhydroxyphenolic compounds in which at least two of the phenolic hydroxyl groups are ortho to each other and which contain one or more carboxyl r sulionic acid groups which are not conjugated or directly attached to the aromatic ring containing said hydroxyl groups. Such compounds constitute the class represented by the following general formulas:

R -OH R OH and Rh Re Rb Re I R R I C O 011 S 03H where R, R R may be alkyl groups, NH -OR -OH,

0 ll 00R- or H. R may be an alkyl group or any carbon chain terminated by a carboxyl, amino or other suitable functional group. R may be NRi or any --(CR R group where R may be H, an alkyl group, R may be an alkyl group (e.g., --CH 11:1, 2, 3. R or R maybe H, any alkyl group, NH OH or other suitable substituent.

Hereinafter, for convenience in terminology, we will refer to the above stated class as the DHPAA group, since DHPAA (3,4-g1ihydroxyphenylacetic acid) is the parent compound of the carboxylic acids in the class, in which event in the above formula R R R are. H and R is CH i.e.,

(3H, (IJOOH Examples of other members of this DHPAA group are 3,4-Qihydroxybetaphenylpropionic acid (DHPPA) and 3,4-dihydroxyaniline-N-methylsulfonic acid. DHPAA can be synthesized readily by demethylation of homoveratric acid with hydobromic acid. A synthetic procedure for DHPPA from catfeic acid is hereinafter mentioned. 3,4-dihydroxyaniline-N-methylsulfonic acid, hereinafter termed DHAMSA can be synthesized from 1-amino-3,4- dihydroxybenzene, formaldehyde and sulfur dioxide.

The use of members of the DHPAA group is advantageous over the use of protocatechuic acid in that the density of the protooattechuic acid mark is limited and may not be increased by the addition of oxidizing agents such as sodium chlorate. This is due to the fact that the mark produced by protocatechuic acid is a direct precipitation of a complex compound formed from Fe ions and protocatechuic acid. Such a mark is distinguished from the mark made from a marking compound in accordance with the present invention which results from the oxidation of the marking compound by Fe ions followed by the release of Fe ions. These Fe ions are oxidized to the Fe state in situ if an oxidizing agent such as sodium chlorate is present. The Fe ions thus produced are then free to react with additional marking compound producing a greater density than otherwise would be obtainable.

The reason for the lack of oxidation of protocatechuic acid by Fe ions is the deactivating effect of the carboxyl group which functions to remove electrons from the ring as indicated by the following resonance forms:

This is directly experimentally demonstrable for the equivalent case of caflfeic acid (3,4-dihydroxycinnamic acid),

COOH

in which the carboxyl group is still conjugated, i.e., electronically connected, to the ring. The indicated resonance forrnsare:

-0H --OH I 1 ylpropionic acid, DHPPA.

electronically connected, to the ring. The double bond in the side chain in caffeic acid may be considered analogous to an electrical wire connecting the carboxyl group to the ring. Reduction of the bond with hydrogen cuts the wire and thereby removes the deactivating effect on the ring that is present in caffeic acid. DHPPA gives extremely high density marks when used in conjunction with oxidizing agents such as NaClO The general concept of the invention is the use of the class of polyhydroxyphenolic compounds in which at least two of the penolic hydroxyl groups are ortho to each other and which contains one or more carboxyl or sulfonic acid groups which are not conjugated or directly attached to the aromatic ring containing said hydroxyl groups. As in PCA, the carboxyl or sulfonic acid group serves to prevent the phenomenon of transfer. Also, as in PCA, it is found that these compounds may be used with metal chloride or bromide electrolytes without the appearance of streaking in copy made from such formulations. However, in contrast to PCA or cafleic acid, the addition of oxidizing agents such as NaClO to these compounds gives formulations which give extremely increased density marks. Also, in contrast with PCA and caffeic acid the elimination of the electron withdrawing effect of the conjugated carboxyl group greatly increases the water solubility. The difference in marking density may be seen by referring to the curve in which optical density is plotted with respect to current. Curve #1 shows the density obtained by the use of DHPAA, curve #2 shows the density using PCA, curve #3, which substantially follows curve #2 shows PCA with sodium chlorate, and curve #4 shows DHPAA with sodium chlorate. It should be noted that the addition of sodium chlorate to, PCA has little or no eifect, while the addition of the sodium chlorate to the DHPAA has a very pronounced effect. The data for the curves was obtained by evaluating the optical density of electrolytically marked paper sheets which had been imprengated with solutions having the following formulations:

In accordance with another aspect of the invention there is provided a graphic recording medium comprising a support treated with a quantity of marking compound chosen from the DHlAA group as an electroresponsive compound for marking the support.

Also in accordance with the invention there is provided an electrolytic recording method and media in which the recording medium comprises an inert, porous and preferably white support, such as a sheet of paper having a high wet-strength, which is impregnated with an aqueous solution of a compound from the DHPAA group and an electrolyte. The electrolyte may be a nitrate but preferably is a chloride or a bromide. The impregnant'may also include a stabilizer and may also include an acidifier, and one or more antifringing agents.

Recording paper may be impregnated with any of the following formulations which are given by way of example:

Example #5 7 Sodium chloride grams 400 DHPAA do 200 Thiourea do 20 Water cc 4000 6 Example #6 Sodium chloride grams 400 DHPAA do 200 Thiourea do 20 Monosodium phosphate do 4 Water cc 4000 Example #7 Potassium nitrate grams 400 DHPAA do 200 Thiourea do 20 Water cc 4000 Example #8 Sodium chloride grams 400 DHPAA do 200 T hiourea do 20 Sodium chlorate do Water cc 4000 Example #9 Sodium chloride grams 400 DHPAA do 200 Thiourea do 20 Monosodium phosphate do 4 Sodium chlorate do 100 Water cc 4000 Example #10 Potassium nitrate grams 400 DHPPA do 200 Thiourea do 20 Sodium chlorate do 100 Water cc 4000 Example #11 Sodium chloride lgrams 400 DHPPA do 200 Thiourea do 20 Water cc 4000 7 Example #12 Sodium chloride grams 400 DHPPA do 200 Thiourea do 20 Monosodium phosphate do 4 .Water cc 4000 Example #13 I "Potassium nitrate grams 400 DHPPA do 200 Thiourea do 20 Water cc 4000 Example #14 Sodium chloride grams 400 DHAMSA do 200 Thiourea do 20 Water cc 4000 Example #15 Sodium chloride grams 400 DHAMSA do 200 Thiourea do 20 Sodium chlorate do 100 Water cc 4000 In the above examples, the quantities given for the marking compounds may be varied up to the solubility limits thereof which are approximately 40 grams per 100 cc. of solution. v V

In the examples the sodium chloride electrolyte may vary from zero to about 1200 grams (the solubility limit) depending upon the degree of electrical conductivity desired, and the potassium nitrate electrolyte may similarly vary from Zero to1200 grams. The sodium chloride may be replaced, without obtaining streaking, by sodium bromide or by any of the chlorides or bromides of any metal the ions of which do not react with the other components in the solution. Typically, these metals include calcium, potassium, magnesium, cesium, lithium or rubidium. The potassium nitrate may be replaced by any of the above chlorides or bromides, and for certain applications where light sensitivity may be tolerated, the potassium nitrate may be replaced by nitrates of the above metals. Similarly the sodium chloride may be replaced by nitrates of the above metals for those applications where light sensitivity may be permissible.

In the above examples the thiourea serves as a stabilizer for the recorded marks and may be replaced by another suitable stabilizer such as one of the alkyl derivatives of thiourea or dithiobiuret. The thiourea may be varied approximately from grams, below which instability occurs, up to about 360 grams which is the approximate solubility limit for the thiourea.

An acid such as citric acid or sulfuric acid may be used as an acidifier. in the above examples the pH preferably is in the range from about 1.0 to 3.5. With a pH value above 3.5 the mark is apt to change color. The pH may be less than 1.0 in those applications where a lighter mark is acceptable. The monosodium phosphate provides an additional anti-fringing function. It may be varied from zero to about 20 grams, above which the density of the mark becomes appreciably less. In the examples the sodium chlorate used as an oxidizing agent may be varied up to its solubility limit of 100 grams per 100 cc. of solution.

Recording paper may be prepared by passing the porous white paper sheet or other porous support of high wetstrength through a bath prepared in accordance with one of the three above formulae given as examples. Approximately 2.5 to 3.0 cc. of the solution is required per square foot of paper in a typical case. The solution is permitted to distribute itself evenly throughout the paper. The excess impregnant may be removed, as by passing the paper through pressure rolls, so that when ready for use in a recorder machine, the recording paper will have above 40% moisture by weight. In order to retard evaporation, the recording paper is stored in sealed containers until needed.

During the recording process a recorder, such as the type referred to herein, may be employed in which an electric current is passed through the recording paper sandwiched between cathode and anode electrodes in contact with opposite surfaces of the paper. The anode may be composed of iron, stainless steel or some other eroding metal capable of reacting with the marking compound in the solution to form one or more colored complex compounds which constitute the recorded color marks on the paper or other support. The recorded paper may then be dried in the air or by some heating device, and the recorded marks will be permanently set. Although not required in order to obtain adequate density of the marks on recording media in accordance with the invention, nevertheless a special heater such as disclosed in U.S. Patent No. 2,485,678 may be employed with the recorder if desired.

Certain specific combinations, materials and specifications have been given by way of example. Various other modifications may be made. For example, formulations containing the marking compounds disclosed herein may also contain, in accordance wtih the present invention, one or more other marking compounds in addition to obtain any further improvement desired.

It will now be apparent to those skilled in the art that various changes and modifications may be made Within the spirit and scope of the invention as defined by the appended claims.

We claim:

1. An electrolytic recording medium comprising an impregnated sheet containing in an electrolytically con- C3 ducting solution as a marking compound a polyhydroxyphenolic acid compound selected from the class consisting of where m indicates the number of phenolic hydroxyl groups attached to the ring at least two of which are ortho to each other and m is an integer from 2 to 4, wherein R and R are selected from the group consisting of H, NH OH and lower alkyl radicals and R is selected from the group consisting of lower alkyl radicals, and where n is an integer from 1 to 6.

2. An electrolytic recording medium comprising an impregnated sheet containing as a marking compound at least one compound selected from the class represented by the following general formula U(OUHZHO O OH) p wherein n is an integer from 1 to 6, p is 0 or 1, and q is an integer from 1 to 6.

3. An electrolytic recording medium according to claim 1 in which the marking compound is 3,4-dihydroxyphenylacetic acid.

4. An electrolytic recording medium according to claim 1 in which the marking compound is 3,4-dihydroxy-beta phenylpropionic acid.

5. An electrolytic recording medium according to claim 1 in which the marking compound is 3,4-dihydroxyaniline- N-methylsulfonic acid.

6. An electrolytic recording medium according to claim '1 in which the pH of the impregnant is in the range of 1.0 to 4.0.

7. An electrolytic recording medium according to claim 1 in which the solution contains at least one compound selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, citric acid and salts thereof, oxalic acid and salts thereof, and formic acid.

8. An electrolytic recording medium according to claim 1 in which a stabilizer is incorporated against degradation in the moist condition prior to marking.

9. An electrolytic recording medium according to claim 1 in which a stabilizer is incorporated and is selected from the group consisting of thiourea, alkyl derivatives of thiourea, and dithiobiuret.

10. An electrolytic recording medium according to claim 1 in which the electrolyte is selected from the group consisting of chlorides and bromides of sodium, calcium, potassium, lithium, magnesium, rubidium and cesium.

11. An electrolytic recording medium according to claim 1 in which is incorporated an oxidizing agent selected from the class consisting of metal chlorates, perchlorates, 'bromates, iodates, and periodates.

12. An electrolytic recording medium according to claim 1 in which is included a stabilizer, and an oxidizing agent, the impregnant consisting essentially in am roxirnate parts by relative Weights of marking compound 15, electrolyte 40, said stabilizer 1, and said oxidizing agent 4.

13. An electrolytic recording medium according to claim 1 in which is included a stabilizer, and an oxidizing agent, the impregnant consisting essentially in approximate parts by relative Weights of 3,4-dihydroxypheny1- acetic acid 1, sodium chloride 40, citric acid 1, said stabilizer being thiourea 1, and said oxidizing agent being sodium chlorate 4.

14. An electrolytic recording medium according to claim 1 in which is included a stabilizer, and an oxidizing agent, the impregnant consisting essentially in approximate parts by relative weights of 3,4-dihydroxybetaphenylpropionic acid 1, sodium chloride 40, citric acid 1, said said stabilizer being thiourea 1, and said oxidizing agent being sodium chlorate 4.

15. An electrolytic recording medium according to claim 1 in which is included a stabilizer, and an oxidizing agent, the impregnant consisting essentially in approxirnate parts by relative weights of 3,4-dihydroXyaniline-N- methylsulfonic acid 1, sodium chloride 40, citric acid 1, said stabilizer being thiourea 1, and said oxidizing agent being sodium chlorate 4.

References Cited in the file of this patent UNITED STATES PATENTS Hogan et a1 Jan. 18, 1944 Mandel Mar. 6, 1962 OTHER REFERENCES UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,,123 542 1 March 3,, 1964 Gerald Mandel et al, It is hereby certified that error appears in' the above numbered bat ent requiring correction and that the said Letters Patent should read as corrected below.

Column .2 line 32, for "electrolyte"""read e-f electrollytic column 3, line 71, for "hy'dobromic" read hydrobromic column 5, line 38 for "impre ngated" read impregnated column 6 line 31, for "DHPPA"' ;reade -j-DHPAA "1*; Column 7, line 42 for "above" rea:1 about;

Signed and sealed this 7th day of July 1964,

(SEAL) Attest:

ERNEST w; SWIDER e EDWA D J. BRENNER Anesting Officer (lom'nliissionerof Patents 

1. AN ELECTROLYTIC RECORDING MEDIUM COMPRISING AN IMPREGNATED SHEET CONTAINING IN AN ELECTROLYTICALLY CONDUCTING SOLUTION AS A MARKING COMPOUND A POLYHYDROXYPHENOLIC ACID COMPOUND SELECTED FROM THE CLASS CONSISTING OF 